R. Dapper

Nursery grounds of dab (Limanda limanda L.) in the southern North Sea

Abstract The distribution of 0-group dab, Limanda limanda L., in the open North Sea, the Dutch coastal zone and the estuarine Wadden Sea was investigated and patterns of seasonal abundance and growth were compared. The purpose was to locate the nursery grounds of dab and to assess their relative importance. Settlement was observed in the North Sea, both in coastal and offshore waters. Highest densities of 0-group dab were found in coastal areas. Since the coastal zone covers only a relatively small part of the North Sea it is not necessarily the most important nursery area for dab. No settlement of dab occurred in the Wadden Sea. Large numbers of juveniles were caught in the tidal channels and subtidal areas in autumn, but their size range indicated that migration rather than settlement was responsible for the observed increase in numbers. A similar process of inshore migration occurred in shallow coastal waters in October. Growth of 0-group dab was more or less similar in all areas. Mean length increased to 6–7 cm by the end of the first year of life.

On the ecology of the dragonet Callionymus lyra L. in the southern North Sea

Abstract The present paper evaluates data collected in the southern North Sea between 1972 and 1984 on geographical distribution, density, growth, mortality, biomass, production and food requirements of the dragonet Callionymus lyra L. Catches never exceeded 1500 individuals per 10 000 m2 and the dragonet showed a clear pattern of abundance with highest densities in the coastal zone and decreasing numbers going offshore. Mortality rates appeared to be rather constant over the age groups with z = 0.55 y−1. The dragonet population mainly consisted of 1, 2 and 3-year-old individuals with a mean length at the end of the year of 7.5, 15 and 19 cm, respectively. Production values were at least 159 g AFDW·10 000 m−2·y−1. Predation pressure exerted by the dragonets amounted to at least 795 g AFDW·10 000 m−2·y−1. The correspondence between the von Bertalanffy growth curve in this study and that of 1948 ( Chang , 1951) suggests absence of effects of eutrophication in the area on the growth of dragonets between 1948 and 1980s. The main difference with 1948 was the absence of large individuals, probably as a result of increased fishery in the area.

Intertidal fish traps as a tool to study long-term trends in juvenile flatfish populations☆

Abstract The suitability of intertidal fish traps (fykes, komfykes and koms) to study long-term trends in juvenile flatfish (plaice, flounder, dab and sole) was analysed with respect to effects of location, type of trap and fishing duration. For all species, catches by the three different types of fykes and on the three locations studied differed considerably, but the patterns over time were approximately the same. The results further suggest that komfykes have the highest catches of flatfish and koms the lowest. The similarity in fluctuations of catches between fish traps and between locations suggest that they may be suitable for the study of long-term changes in flatfish populations. For all species, increasing fishing duration from 24 to even up to 96 h hardly resulted in higher catches.